Cornea implant

ABSTRACT

Annular cornea implant for inserting into a cornea pocket of the human eye via a narrow, tunnel-shaped access, with the end shape of the cornea implant depending on the shortsightedness or astigmatism to be corrected. The aim of the invention is to enable the cornea implant to be implanted in the cornea pocket in a simple manner and in an optimum position. To this end, the implant has a shape memory which is impressed on the basis of the geometry and/or material of the implant, and is designed in such a way that the deformability from a starting shape enables the insertion of the cornea implant into the cornea pocket via the narrow access, and the cornea implant has an adjustment force in the end shape thereof, which enables an essentially independent unfolding of the cornea implant in the cornea pocket.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the National Stage of PCT/AT2007/000130 filed onMar. 16, 2007, which claims priority under 35 U.S.C. §119 of AustrianApplication No. A 428/2006 filed on Mar. 16, 2006. The internationalapplication under PCT article 21(2) was not published in English.

AREA OF THE INVENTION

The present invention relates to an annular cornea implant for insertinginto a cornea pocket of the human eye via a narrow, preferablytunnel-shaped access, with the end shape of the cornea implant dependingon the refractive error to be corrected.

STATE OF THE ART

The optical apparatus of the human eye for depicting the environmentbasically consists of the cornea and the lens which is positioned behindthe iris. This optical apparatus of the eye has a total refractive powerof approximately 60 dioptres, with the interface between the cornea andthe air—i.e. the outer boundary of the eye—with approximately 40dioptres accounting for most of the refractive power. This refractivepower of the cornea is basically indirectly proportionate to the radiusof the cornea surface (interface between cornea and air). A change inthe radius of the curvature of the cornea also leads to a change in therefractive power of the eye. By increasing the (central) radius ofcurvature of the cornea the refractive power decreases, a fact which theeye surgeon takes advantage of in refractive surgery for the correctionof shortsightedness. The refractive surgical techniques using laser(LASIK, LASEK, etc.) remove more corneal tissue from the central partsthan from the peripheral parts of the cornea.

With the LASIK technique, for instance, a lamellar “flap” is cut intothe cornea at a certain depth. Such flaps have the major disadvantagethat they significantly impair the biomechanical stability of thecornea. The flap, in particular, no longer fully adheres to theunderlying corneal tissue. This reduces the bio-mechanically effectivecross section of the cornea by exactly the amount that corresponds tothe thickness of the flap. The preferable option would be to undertakecorrective measures on the inside of the cornea, without risking such amassive biomechanical impairment as is caused by a flap. Moreover, thelaser techniques mentioned above are only suited for the treatment ofmyopic patients with up to 10 dioptres.

To avoid these drawbacks, methods have been developed in which corneaimplants are used that cause a deformation of the cornea to the effectthat the radius of curvature of the cornea is enhanced by adding volume,which in turn reduces the refractive power and thus corrects the myopiceye.

Cornea implants are mostly annular or ring-shaped, using either fullrings (open or closed) or parted rings (e.g. ring segments).

US 2005/0119738 A1, for example, reports the use of such a corneaimplant underneath a flap. It describes an annular implant for insertioninto the cornea underneath a flap. In this case, a central part of thecornea implant is directly optically effective, i.e. in order to fulfillits task, it must be part of the optical zone and be penetrated by therays of light to be depicted. The cornea implant has the task to form amultifocal corneal surface, with the area of the central hole in thecornea implant being responsible for near vision and the area that alsoincludes the inner part of the cornea implant (optical zone) for farvision. To be able to solve this difficult task, the optical zone(including the inner part of the cornea implant) must be located withinthe diameter of the pupil of the eye, which is mostly 2 to 5 mm. Theinner hole of the cornea implant therefore must not be essentiallylarger than 2 mm. Moreover, the inner part of the cornea implant, whichis intended to be directly involved in producing an image in far vision,must have a minimum width which, taking account of the optical laws,must substantially exceed 1 mm (2 mm) in order to be effective. Added tothis is the outer part of the cornea implant. This results in thesubstantial problem that the significant material width, which by farexceeds 1 mm, may lead to problems with oxygen and nutrient supply.While the problem with nutrient supply may be ameliorated by using themicroporous hydrogel indicated, problems with stability andstabilisation of the ring geometry still tend to arise due to thesoftness of the ring.

Moreover, the cornea implant has no pointed end on its inner or outeredge, but a finite edge thickness of preferably 10 μm. These edges havethe considerable disadvantage that deposits may occur in the area,leading to vision impairment.

Experience with multifocal imaging, both in contact lens adjustment andin the implantation of intraocular lenses in cataract surgery, showsthat this is tolerated by only a small minority of patients. Themajority of patients perceive the simultaneous “blur” of the focal pointalong the optical axis as disturbing rather than beneficial. Moreover,it is to be expected that with respect to the present structure,patients will perceive the central part of the cornea implant, and herein particular the inner edge that needs to lie within the pupil width,as disturbing (despite adjustment to the refractive index of thesurrounding medium).

As can be seen, the insertion of a cornea implant into the corneaunderneath a flap has considerable drawbacks and in particular resultsin a significant impairment of the stability of the cornea on account ofthe lamellar cut in the cornea for producing a flap. This impairment ofthe stability of the cornea is typically experienced in LASIK surgery,where a similar flap needs to be created.

Ring-shaped cornea implants are also used in conjunction with techniquesenvisaging a circular incision in the corneal surface. GB 2095119 A, forinstance, describes such a circular incision from the corneal surfaceinto the corneal tissue, into which a ring of approximately 8 mm indiameter is introduced for the purpose of flattening the central cornea,which leads to myopia correction. Two different ring geometries aredescribed and reference is made to their size. A circular ring sectionwith a thickness of approx. to 0.5 mm and a triangular ring section withan edge length of approx. 0.3 mm. The materials mentioned areessentially polymer plastics. The disadvantage of this method is thesignificant traumatisation of the tissue. After inserting the ring intothe corneal tissue, for instance, the incision needs to be closed with asuture along the full length of the circumference as otherwise the ringcould not be maintained in a stable position inside the cornea, and thestability of the cornea would be massively impaired. Without a suture,the extent of correction, i.e. the dioptres treated, would not becontrollable. But even with a suture, the extent of correction can onlybe foreseen to a certain extent if the ring is rigid enough and onlymarginally deformable to withstand a potential pull of the tissueresulting from the suture.

WO 93/12735 A1 describes a variant of GB 2095119 A with abio-compatible, annular cornea implant, which is also inserted into thecorneal stroma through a circular incision in the corneal surface forthe purpose of correcting the refractive power in the myopic eye. Saidimplant is a ring with a fixed, i.e. unchangeable diameter, a refractiveindex that does not deviate from that of the corneal tissue by more than2% and may have the following dimensions: ring diameter approx. 2.4 mmto 12 mm, ring width approx. 0.2 mm to 4 mm and ring thickness approx.0.005 to 0.2 mm. The ring has a convexly shaped front side and a flatback side. In this case, too, the traumatisation of the tissue wheninserting the implant is considerable. Another major drawback when usingthe implant inside the cornea is the flat back side of the ring. Sincethe corneal surface is curved with a radius of approx. 8 mm, this leadsto the fact that with the ring widths indicated the shape of the backside of the ring and the corresponding corneal cut inside the corneapocket are in part considerably different from each other. Such adisproportionate geometry may, as frequently described in theliterature, lead to massive accumulation of deposits of organic materialalong the interfaces, which may lead to vision impairment andundesirable cosmetic results. Moreover, this results in a highly unevendistribution of pressure on the tissue across the back face of the ring,which may induce pressure atrophies and tissue necrosis.

To avoid the disadvantages described above, methods have been developedwhere the respective cornea implant is inserted into a fully enclosedcornea pocket via a narrow, tunnel-shaped access. Since the innertension of the cornea acts alongside the corneal lamellae, the formationof a basically enclosed cornea pocket does not reduce thebio-mechanically effective cross section for this tension and thebio-mechanical stability of the cornea is not impaired.

A suitable procedure and a suitable device for creating such a corneapocket is, for instance, described in EP 1 620 049 B1, the content ofwhich is therefore adopted in this application.

The creation of such a cornea pocket including a narrow, more or lesstunnel-shaped access is, however, already known from US 2002/0055753 A1.After its insertion into the cornea pocket, the folded annular corneaimplant is unfolded and placed in position. Although the insertion via anarrow tunnel works really well with these highly flexible, foldablecornea implants, this well-known procedure and the cornea implantsinserted therewith have the decisive disadvantage that said implant hasto be manually unfolded inside the pocket after insertion. However, amultitude of forces are effective inside the pocket after insertion ofthe cornea implant which prevent the cornea implant from unfoldingitself, so that especially in the case of very flexible rings, there isa risk that the cornea implant does not resume its original predefinedshape after implantation and astigmatisms or higher-order aberrationsmay be induced. Tedious, complicated manual manipulations therefore needto be taken into account after implantation to restore the initial ringform. But resuming the exact shape is often impossible and so thedesirable correction of the refractive error may not be achieved.Moreover, the need for the cornea implant to be manually unfolded in thecornea pocket puts the cornea itself and above all the narrow,preferably tunnel-shaped access into the cornea pocket under unnecessarystrain. In other words, a sufficiently flexible state-of-the-art corneaimplant may facilitate the insertion into the cornea pocket via thenarrow access, but simultaneously complicates the unfolding inside thecornea pocket.

The task of the present invention therefore is to create a corneaimplant which has none of the drawbacks described above and may be usedin a vision correction procedure, where a cornea implant is insertedinto a cornea pocket via a narrow, preferably tunnel-shaped access.

DESCRIPTION OF THE INVENTION

According to the invention, this is achieved through the characterisingfeatures of claim 1.

The aim of the invention is that the annular cornea implant forinserting into a cornea pocket of the human eye via a narrow, preferablytunnel-shaped access, with the end shape of the cornea implant dependingon the refractive error to be corrected, has a shape memory which isimpressed on the basis of the geometry and/or material of the implant,and is designed in such a way that the deformability from a startingshape enables the insertion of the cornea implant into the cornea pocketvia the tunnel-shaped access and the cornea implant has an adjustmentforce in die end shape thereof, which enables an essentially independentunfolding of the cornea implant in the cornea pocket.

According to a preferred embodiment of the invention, the starting shapeand the end shape are identical.

To avoid an impairment of the biomechanical stability of the cornea asresults when cutting a flap, the width of such a tunnel-shaped access toan otherwise closed cornea pocket should typically not exceed 5 mm, andideally lie between 2 mm and 3 mm. A cornea implant according to theinvention may therefore be inserted into the cornea pocket via a narrowaccess, the maximum width of which is below 5 mm, and preferably between2 mm and 3 mm, to avoid an impairment of the biomechanical stability ofthe cornea as results when cutting a flap, without breaking or beingaltered in its shape (such as by permanent (irreversible) plasticdeformation).

At the same time it is assured that the cornea implant, in addition tobeing sufficiently deformable, also has the ability to create anadequate adjustment force so as to safely unfold into a predefinedform—its end shape—inside the cornea pocket after implantation. Itunfolds more or less independently and automatically, without anyadditional or essential, additional manual interference.

A precondition for this is that on account of the impressed shapememory, one or several optional end shapes may be pre-programmed in thecornea implant according to the invention, and the latter, being eitherplastically or elastically deformed, assumes one of these end shapeseither automatically or through activation by a trigger signal.

The shape memory is either impressed on the basis of a suitable chosenmaterial, or on the basis of a special geometry of the cornea implant,or on the basis of a material-geometry combination.

The materials suited for insertion may be elastically or non-elasticallydeformable (plastic) materials. In elastic materials with a shapememory, the deformability and adjustment force mainly results from theelasticity of the material, such as PMMA (polymethyl methacrylate),silicone, etc. In non-elastic materials such as shape memory alloys, theadjustment force results, for example, from atomic forces which arereleased when one grid structure is spontaneously transformed intoanother.

Basically, there is a multitude of materials with a shape memory, whichfacilitate a shape memory of the cornea implants according to theinvention. These include PMMA, polymers of EEMA or HEMA, or otheracrylic materials, hydrogels, nylon, polycarbonate, polyethylene orother plastics, plastics with a temperature-dependent shape memory,shape memory alloys (e.g. based on Ni—Ti, Cu—Zn—Al, Cu—Al—Ni, etc.),suitable compounds of plastics and metals or non-metals (e.g. ceramics,semi-conductors, etc.), suitable compounds of metals and non-metals(e.g. ceramics, semi-conductors, etc.), or composite materials. Some ofthese materials, such as hydrogels, have already been used in corneaimplants, but only the conditions under which they are applied and inparticular the geometry of the cornea implant lead to the impression ofthe desirable shape memory.

It is important to assure that the desirable end shape can be achieved,by means of the adjustment force, from the intermediary shape into whichthe cornea implant needs to be deformed in order to be able to beinserted into the cornea pocket via the narrow access, irrespective ofwhether the starting shape and the end shape are identical or not.

The task according to the invention may, as mentioned before, also besolved exclusively or additionally by envisaging a special geometry ofthe cornea implant.

Therefore also known elastic materials may be used as corneaimplantation body, which receive the desirable shape memory due to theirgeometrical design.

An exact fitting of the adjustment force is of vital importance becausethe cornea implant is only in its end shape suited to correct therespective refractive error. If the end shape cannot be achieved or isnot exactly achieved, the correction of the refractive error is alsoinadequate.

After being implanted into the cornea pocket, the cornea implant isexposed to considerable forces that act against its unfolding, such asthe frictional forces resulting from the pocket walls between which thecornea implant is positioned. This is further enhanced by forcesresulting from the intrinsic tension of the cornea and the intraocularpressure.

The impression of a shape memory alone is therefore insufficient, and itmust additionally be guaranteed that the—pre-programmed—end shape isachieved by means of an adjustment force that is suited to overcome theforces acting against the unfolding of the implant to obtain its endshape.

According to another preferred embodiment of the invention, the materialsuited for impressing the shape memory is a material with a shape memorythat can be activated, preferably a material with an electrically,thermally, mechanically or magnetically activable shape memory.

This enables the cornea implant, once implanted, to be readjusted at anytime, with the possibility that the activation may also lead todifferent end shapes.

When using materials with a thermally activable shape memory accordingto the invention, the cornea implant may also adopt its desirable endform after plastic deformation. In a preferable embodiment of theinvention, this is achieved by the targeted use of shape memory alloys.

By using materials with an activable shape memory as cornea implantaccording to the invention, it is moreover possible that the insertedcornea implant having reached its end shape may further change its endshape even after implantation, for example, by being activated throughan electric or magnetic field created from outside or by having anelectric current pass through it.

The group of materials with shape memory according to the invention alsoincludes those which may change their size, or elasticity, or plasticityin the wake of swelling or deswelling, such as by absorption orextraction of water. Such materials may include completely orincompletely hydrated plastics, such as HEMA or hydrogels.

There are also materials with a shape memory where the end shape can beactivated and adjusted by mechanical signals (e.g. by using ultrasoundor reducing the frictional forces inside the pocket) or by chemicalsignals (e.g. change in pH value).

According to an alternative embodiment of the invention, the materialswith a shape memory are shape memory alloys, for example those based onNi—Ti, Cu—Zn—Al and Cu—Al—Ni. According to a preferred embodiment, suchcornea implants are wrapped in an inert, biocompatible protective layer.

To enable a particularly exact automatic unfolding inside the corneapocket, there is yet another preferred embodiment of the invention,according to which the choice of a suited material and the respectiveadjustment to the geometrical form of the annular cornea implant assuresthat the deformability of the cornea implant is at least 25 percent inat least one outer dimension of the ring, preferably the ring diameter,and the cornea implant has an adjustment force (or restoring force) intothe original ring form (or desired end shape) in the range of 0.001N to1N, ideally between 0.01N and 0.5N, in at least one direction (thedirection of deformation), but ideally in all directions.

A particularly preferable geometrical form of the annular cornea implanthas proven to be a cornea implant shaped like a circular ring with anouter diameter ranging between 4 mm and 12 mm, a ring width between 0.4mm and 1.5 mm, preferably 0.5 mm, and a ring height between 0.01 mm and0.8 mm. To this end, the inner diameter of the ring should not liewithin the pupil width to avoid the perception of disturbing effects atthe border.

The front face of the cornea implant is preferably convex and the backface preferably concave. This assures that the pocket wall more or lessflawlessly adheres to the cornea implant, with the front and back faceof the ring seamlessly flowing into each other at the edges.

On account of the good deformability and sufficient adjustment forceaccording to the invention, the cornea implant may also have the shapeof a closed or split ring and still be inserted into the cornea pocketvia the narrow access without difficulty. The shape of a closed ringguarantees that the cornea implant, after being implanted in the corneapocket, resumes an annular, undistorted and stable ring form.

The cornea implant may have the form of a circular ring as its end shapefor the correction of shortsightedness, or a non-circular ring form forthe correction of other refractive errors, such as astigmatism in thecase of an elliptic ring form.

Reference to additional preferred embodiments of the invention is madeunder the sub-claims listed below.

SHORT DESCRIPTION OF THE DRAWINGS

The following is a detailed description of the invention using examplesof embodiments. The figures show the following:

FIG. 1 a sectional view of a cornea implant according to the invention

FIG. 2 a cornea implant according to the invention which has beendeformed for the purpose of inserting it via a tunnel-shaped access

FIG. 3 a cornea implant according to the invention with differentannular cross sections along the circumference

FIG. 4 a cornea implant according to the invention with a saddle-shapedring geometry

FIG. 5 a a cornea implant according to the invention with an annularshape

FIG. 5 b a cornea implant according to the invention with a differentannular shape

FIG. 6 a a cornea implant according to the invention with a first crosssection

FIG. 6 b a cornea implant according to the invention with a second crosssection

FIG. 6 c a cornea implant according to the invention with a third crosssection

FIG. 6 d a cornea implant according to the invention with a fourth crosssection

FIG. 6 e a cornea implant according to the invention with a fifth crosssection

FIG. 6 f a cornea implant according to the invention with a sixth crosssection

FIG. 6 q a cornea implant according to the invention with a seventhcross section

FIG. 6 h a cornea implant according to the invention with an eighthcross section

FIG. 6 i a cornea implant according to the invention with a ninth crosssection

FIG. 6 j a cornea implant according to the invention with a tenth crosssection

FIG. 7 a a front perspective view of a cornea implant according to theinvention having the shape of a closed circular ring

FIG. 7 b a front view of a cornea implant according to the inventionhaving the shape of a closed circular ring

FIG. 7 c a rear perspective view of a cornea implant according to theinvention having the shape of a closed circular ring

FIG. 7 d an elevational view of a cornea implant according to theinvention having the shape of a closed circular ring

FIG. 8 a a front perspective view of a cornea implant according to theinvention having the shape of a split circular ring

FIG. 8 b a front view of a cornea implant according to the inventionhaving the shape of a split circular ring

FIG. 8 c a rear perspective view of a cornea implant according to theinvention having the shape of a split circular ring

FIG. 8 d an elevational view of a cornea implant according to theinvention having the shape of a split circular ring

FIG. 9 a a cross section of an annular cornea implant according to theinvention with a central lens body

FIG. 9 b a front view of the annular cornea implant with a central lensbody shown in FIG. 9 a

FIG. 10 illustration of an implantation process where an annular corneaimplant according to the invention is inserted into a cornea pocket viaa narrow tunnel

WAYS TO EXECUTE THE INVENTION

As seen in FIG. 1, a cornea implant according to the invention comprisesan annular ring body 5, which has a convex front face 1 and a concaveback face 2. The concavity of the back face 2 may be spherical oraspherical, such as by approximation via several spherical curvatures.The centres of curvature 3 of the radii of curvature 10 of the two backface sections 2 a,2 b are preferably arranged alongside the axis 4 ofthe cornea implant according to the invention. In aspherical back faces,several centres of curvature 3 are arranged alongside the axis 4, whichcorresponds to the optical axis.

Apart from allowing a perfect adjustment of the back face of the ring tothe implantation bed and preventing the formation of deposits andpressure atrophies in the tissue, this also drastically increases thedeformability of the rings, without reducing the adjustment force in thesame way.

The outer diameter 6 of the cornea implant is preferably in the range of4 mm to 12 mm, ideally between 5 mm and 9 mm. The inner diameter 11 ispreferably in the range of 3 mm to 11 mm, ideally between 4 mm and 8 mm.The ring width 8 is ideally 0.5 mm, ought to be less than 1 mm to ensurea proper nutrient supply, and is preferably between 0.4 mm and 1.5 mm.

The ring height 9 is in the range of 0.01 mm to 0.8 mm, ideally between0.1 mm and 0.4 mm.

The inner diameter 11 of the cornea implant should in any case be widerthan the respective pupil width to avoid effects at the border which thepatient may find disturbing.

The front and back faces 1 and 2 flow seamlessly into each other at theedges.

The back face 2 ideally follows the natural course of the correspondingpocket wall inside the cornea (local corneal radii minus pocket depthplus (or by) correction factor, which considers the deformation of thecornea resulting from the insertion into the pocket), so that theconcave progression of the back face of the ring corresponds to aspherical or aspherical curvature, with radii 10 lying between 4 mm and40 mm, preferably between 6 mm and 10 mm.

According to the invention, the cornea implant 5 has a shape memorywhich is impressed on the basis of its material and/or geometry anddesigned in such a way that the cornea implant has a deformability froma starting shape, which enables the insertion of the cornea implant intothe cornea pocket via the narrow, preferably tunnel-shaped access withan inner width of less than 5 mm and concurrently has an adjustmentforce in the end shape thereof, which enables an essentially independentunfolding of the cornea implant in the cornea pocket.

The preferred materials for this purpose may include plastics such asPMMA, HEMA, silicone, polycarbonates, polyethylene or other polymerplastics or shape memory alloys.

FIG. 2 shows a cornea implant according to the invention, which islaterally compressed by force, as symbolised by the arrows 12, to beable to be inserted via the narrow access (not included) into a corneapocket.

With respect to the elastic deformation of materials, the adjustmentforce is in general reciprocally proportionate to the deformability.

When using materials which are only elastically deformable within a verynarrow deformation range (e.g. PMMA), it is essential to give the corneaimplant a special shape by which it becomes sufficiently deformable yetalso retains its restoring force.

In the case of a cornea implant as illustrated in FIG. 2, this isachieved by the special contour line of the back face 2 towards the ringcenter, where the centers of curvature 3 of the radii 10 are arrangedalong the axis 4, thus not only achieving a simple oval shape, but asaddle-shaped object as a part of the ring deviates from the ring level14 into the third dimension 13 when being deformed (compression). Thisgenerates an additional degree of freedom, which considerably increasesthe deformability without essentially reducing the adjustment force.

According to the invention, the deformability must be at least 25percent of a typical annular dimension and the cornea implant has anadjustment force into the original ring form in the range of 0.001N to1N, ideally between 0.01N and 0.5N.

A typical ring dimension in a circular cornea implant, for instance, isthe ring diameter 20, whereas in an elliptic cornea implant, forinstance, it is the minor axis 19 (FIG. 5).

In the embodiments according to FIG. 1 and FIG. 2 it is even possible todeform a ring made of PMMA (a material that is difficult to deform andeasily breaks when being deformed), which has an outer diameter 6 of 5mm, a ring width 8 of 0.5 mm and a ring height 8 of 0.25 mm as well as aradius of curvature 10 of 8 mm, by approximately 50% of its diameter,yet assuring that it does not break and retains a sufficient adjustmentforce to freely and independently resume its original ring geometryafter being implanted in the cornea pocket against the forces resistingits unfolding. In this case, the impression of the shape memory resultsexclusively from a special geometry, whilst the choice of material is ofno relevance.

To enable an exact fitting of the adjustment force, the cornea implantmay have different ring cross sections 15,16 along the circumference, asis illustrated in FIG. 3.

When it has the form of a “saddle”, the basic edges 17, 18 along thering circumference are not on the same level, as can be seen in FIG. 4.

Depending on the refractive error to be corrected, the cornea implant 5according to the invention may have all sorts of different crosssections, as can be seen in FIG. 6.

An exact attuning of the material and geometry of the cornea implant 5to each other assures that the cornea implant may unfold independentlyinside the cornea pocket after insertion.

The respective material may be a material with a shape memory that canbe activated, preferably a material that can be electrically, thermally,mechanically or magnetically activated, such as shape memory alloys.

The trigger signal for such activation may for instance be thetemperature, so that the cornea implant according to the invention issufficiently deformable in a cooled-down condition for inserting it intothe cornea pocket via the narrow, preferably tunnel-shaped access. Thecornea implant warms up inside the cornea pocket until reaching acertain trigger temperature, where the cornea implant resumes its endshape or, being exposed to an adequate adjustment force between 0.001Nand 1N, ideally between 0.01N and 0.5N, approaches its end shape. Sincethe temperature inside the cornea may not be sufficient to achieve thetrigger temperature, heat may also be introduced from outside the eye.

In the case of a material with a shape memory that can be magneticallyor electrically activated, the material may, for instance, containelements based on, or entirely consist of, Ni—Mn—Ga. After thesuccessful implantation in the cornea pocket according to the invention,an adjustment from one end shape into another end shape may be achievedby inducing a voltage to the implant or exposing it to an electric ormagnetic field. This even enables a posterior fine-tuning or adjustmentof dioptres, such as would be necessary if the dioptres of the eye wereto change again over time, without the need to replace the corneaimplant.

In principle, different trigger signals may be used to activate theshape memory, including mechanical or chemical trigger signals. So whenusing certain materials, such as those appropriate due to their elasticdeformability, the assumption of a defined end shape can be fostered byapplying ultrasound or exerting pressure on the cornea implant or thebed of the implant. Moreover, by changing the degree of swelling of theimplant, such as by adding or extracting liquid, the assumption of ashape may be facilitated or a respective activation energy required forobtaining a certain shape may be overcome. Moreover, such a triggersignal may also be released by an intentional pH value change in thetissue surrounding the implant or in the cornea implant proper.

Typical materials with a shape memory that can be activated are forinstance polymer metals, ionic polymer-metal composites, IMPC,electroactive polymers (e.g. electronic or ionic EAP materials) such aspolyacrylonitril (PAN), ceramics or electroactive ceramics, suitedconductor or semi-conductor plastics, ionic polymeric conductorcomposites, IPCC, and magnetic shape memory elements such as those basedon NiMnGa or Ni2MnGa.

Shape memory alloys may be alloys based on Ni—Ti, Cu—Zn—Al, Cu—Al—Ni andother materials. Plastics with a temperature-dependent shape memory aswell as shape memory alloys may be easily deformed (in particular alsoby plastic deformation) preferably below a specific transformationtemperature, but resume a predefined shape above this transitiontemperature. In this manner, changing the temperature of the foldedcornea implant in its intermediate shape may help to achieve itsunfolding into the desired shape after being inserted into the stromalimplantation bed.

Shape memory alloys are characterised by a martensitic phase transition(second-order phase transition), where the material changes itscrystalline structure when a specific transformation temperature isexceeded and assumes a predefined shape. This is an atomic and not amolecular phenomenon, such as in elastic deformation, where mostlypolymer molecules are deformed. When a transformation temperature isexceeded, in fact, the atoms of the material spontaneously adopt anentirely different order. Although some shape memory alloys arebiocompatible, shape memory alloys may be coated with silicone or anyother inert, biocompatible materials (e.g. plastics) to assure that thetissue is not directly exposed to the alloy and thus cannot suffer anydamage. Such cornea implants are also able to create pressure inside thetissue, such as when pressure is exerted against the cutting edges,which may additionally result in any kind of deformation of the cornealsurface. Such cornea implants may have any shape, in particular they maybe open or closed, annular (see FIGS. 7 and 8), elliptic, saddle-shapedwith one or more saddles, spiral-shaped, single- or multi-threaded,curved or straight, etc. The implants may or may not have a plasticcoating. They may be continuous or segmented. They may be furnished withelectrical contact elements. The majority of such elements are alsosuited for implantation into circular tunnels.

FIG. 9 shows an annular cornea implant with a central implantation body21 according to the invention.

When correcting farsightedness, the central corneal radius needs to bereduced. This is why a central implantation body (lens) 21 needs to bechosen where the central thickness is higher than the peripheralthickness, whereas the aforementioned criteria related to the materialof an annular cornea implant without a central implantation bodyinvariably also apply in this case. In particular, a cornea implant isrecommended which is at least partly made of a material with a shapememory or one that can be fine-tuned.

In this case, a central, possibly deformable lens 21, preferably onemade of an elastic, transparent, biocompatible material, is enclosed bya ring body 5 with a shape memory. Because of the central lens and thesurrounding ring being connected with each other, the lens may beinserted into the cornea pocket together with the ring and unfoldedinside the pocket with the help of the ring, according to the invention.This may, for example, be achieved through elastic forces or through theapplication of a certain temperature or an electric voltage or anelectric or magnetic field. The central lens 21 and the ring 5 may beconnected with each other in any way, such as by being welded together,by being wrapped up together in the same foil, by being glued together,by melting the ring into the lens, or by integrating the ring into thelens in any way. The central lens body 21 may, for instance, consist ofhydrogel, HEMA, polyethylene, or any other polymer or non-polymerplastic. It is essential that the lens body is sufficiently permeable tooxygen and/or nutrients. Moreover, it can be elastic or non-elastic. Therefractive index may be of any dimension whatsoever. The lens body 21itself may also contain a shape memory. Embodiments as for an annularcornea implant without a central lens body 21 also apply withoutrestrictions to annular cornea implants with a central lens body 21.

The ring body 5 may, in particular, be produced from any of thematerials described above, including materials where the shape memorycan be thermally, electrically or magnetically activated. This allows,for example, to use an electrically or magnetically readjustable ringbody (as described elsewhere herein) for changing the tension and thusthe central thickness (mean thickness) 22 of the elastic lens body 21,thereby influencing the impact of the latter in correcting therefractive error of the eye. By choosing an appropriate geometry for thecentral lens body 21, such as a diffractive or refractive bifocal ormultifocal lens, also age-related farsightedness (presbyopia) may becorrected. It may, for instance, be designed as a Fresnel lens body. Itmay consist of a partly or fully non-transparent material. It may alsobe designed as a lens body that is not dioptrically effective (e.g.without a central thickening 22). Moreover, if made of a non-transparent(e.g. black) material, it may be effective by producing an image througha single slot or multiple slots, or a single hole or multiple holes(i.e. holes that are arranged in a certain way to achieve a diffractiveeffect). These holes, due to their arrangement, may have a diffractiveeffect or, in case of only one hole, a stenopeic effect. However, theseholes need not be physical holes, but may also be transparent spots inan otherwise non-transparent medium to achieve this effect. Thestatements made, in particular those relating to (open) ring-shapedstructures or segments, not only apply on the basis of the implantationpocket described herein, but also have validity with respect to otherimplantation pockets, especially for complete or segmented annularpockets, such as those used for implanting Intacs.

For the correction of astigmatism, rings (open, closed, split orsegmented) or central bodies with an asymmetrical shape or cross sectionare needed. Myopic astigmatism is therefore most easily corrected byusing a round implant with different cross sections along the main axes,or with a homogeneous cross section but preferably elliptic ring shape,or a combination of both. The same applies to hyperopic astigmatism,with the difference that not the ring but the central body (lens) isasymmetrical, and that this asymmetry is preferably impressed on thebody by one of the aforementioned materials and/or shapes. Inparticular, the central radii of the two main sections of the astigmaticimplantation body are different.

FIG. 10 illustrates the implantation procedure of an annular corneaimplant, according to the invention, being inserted into a cornea pocketvia a narrow tunnel. To this end, an annular cornea implant 5 with anytype of starting shape 23, but preferably one that corresponds to theend shape 26 or 27, is deformed so as to adopt an intermediate shape 24for inserting into the cornea pocket via a tunnel 25. Subsequently,through the shape memory according to the invention which is impressedon the implant 5, the intermediate shape 24 is changed into a predefinedshape 26 (end shape) inside the cornea pocket. This shape preferablycorresponds to the initial starting shape 23, but may also be different.This change of shape may take place automatically or may be triggereddirectly or indirectly via an appropriate trigger signal. Such a triggersignal is ideally a temperature increase in the implant exceeding acertain transformation temperature. Subsequently, the implant may, incertain cases, change from an end shape 26 into another end shape 27.This change from one end shape 26 into another end shape 27 is ideallytriggered by electric or magnetic signals. The end shape 27 may, inparticular, be determined by the electric or magnetic field strengthapplied or by the electric current through the implant 5.

It needs to be stressed that each feature of an embodiment can becombined with any feature of another embodiment, to obtain a newembodiment.

1. Annular cornea implant for inserting into a cornea pocket of thehuman eye via a narrow access to the cornea pocket to correct arefractive error of the eye, comprising: i. a starting shape comprisinga circular or elliptical ring body having a ring width and a ringheight, said ring body further comprising a plurality of startingdimensions disabling insertion of the cornea implant into the corneapocket via the narrow access, said plurality of starting dimensionscomprising a starting shape outer dimension selected from the groupconsisting of a diameter ranging from 4 mm to 12 mm and a minor axisranging from 4 mm to 12 mm, ii. a deformability into an intermediateshape, said intermediate shape being generated from the starting shapeby laterally compressing the cornea implant in such a way to formintermediate dimensions comprising an intermediate shape outer dimensionsmaller than the starting shape outer dimension to enable the insertionof the implant into the cornea pocket via the narrow access, and iii. anadjustment force which enables independent unfolding from theintermediate shape into an end shape to be adopted after inserting thecornea implant into the cornea pocket via the narrow access, the endshape comprising ending dimensions comprising an end shape outerdimension larger than the intermediate shape outer dimension, whereinthe ring body has an impressed shape memory from at least one of amaterial of the ring body and a geometry of the ring body such that inthe starting shape the ring body is disposed in a ring level extendingin first and second dimensions, in the intermediate shape a part of thering body is deviated from the ring level into a third dimensionorthogonal to at least one component of a compression force applied tothe ring body to form the intermediate shape, and after inserting thecornea implant into the cornea pocket via the narrow access the endshape is adopted as a result of independent unfolding of the ring bodycaused by the adjustment force; and wherein the annular cornea implantcomprises an intracorneal implant.
 2. Annular cornea implant forinserting into a cornea pocket in the human eye via a narrow access tothe pocket according to claim 1, wherein the starting shape and the endshape are substantially identical.
 3. Annular cornea implant forinserting into a cornea pocket in the human eye via a narrow access tothe pocket according to claim 1, wherein the intermediate shape outerdimension is at least 25 percent smaller than the starting shape outerdimension.
 4. Annular cornea implant for inserting into a cornea pocketin the human eye via a narrow access to the pocket according to claim 3,wherein the adjustment force is in a range of 0.001 N to 1 N.
 5. Annularcornea implant for inserting into a cornea pocket in the human eye via anarrow access to the pocket according to claim 3, wherein the ring bodycomprises a rigid material.
 6. Annular cornea implant for inserting intoa cornea pocket in the human eye via a narrow access to the pocketaccording to claim 1, wherein the ring body comprises exterior front andback faces, the front face being convex and the back face being concave.7. Annular cornea implant for inserting into a cornea pocket in thehuman eye via a narrow access to the pocket according to claim 1,wherein the starting shape is a closed ring.
 8. Annular cornea implantfor inserting into a cornea pocket in the human eye via a narrow accessto the pocket according to claim 7, wherein the ring body comprisesexterior front and back faces, the front face being convex and the backface being concave.
 9. Annular cornea implant for inserting into acornea pocket in the human eye via a narrow access to the pocketaccording to claim 4, wherein the intermediate shape outer dimension isat least 25 percent smaller than at least one of the diameter, the ringwidth, and the ring height.
 10. Annular cornea implant for insertinginto a cornea pocket in the human eye via a narrow access to the pocketaccording to claim 7, wherein the ring body comprises a rigid material.11. Annular cornea implant for inserting into a cornea pocket in thehuman eye via a narrow access to the pocket according to claim 1,wherein the ring width and the ring height vary circumferentially alongthe ring body.
 12. Annular cornea implant for inserting into a corneapocket in the human eye via a narrow access to the pocket according toclaim 1, further comprising a central body of at least partialtransparency arranged within an inner diameter of the ring body. 13.Annular cornea implant for inserting into a cornea pocket in the humaneye via a narrow access to the pocket according to claim 1, wherein thepart of the ring body deviated from the ring level comprises a limitedrange of a circumferential portion of the ring body, saidcircumferential portion having a cross-sectional area entirely deformedinto the third dimension.
 14. Annular cornea implant for inserting intoa cornea pocket in the human eye via a narrow access to the pocketaccording to claim 1, wherein the ring body comprises a hydrated orpartially hydrated material.
 15. Annular cornea implant for insertinginto a cornea pocket in the human eye via a narrow access to the pocketaccording to claim 1, wherein the intermediate shape outer dimension isat least 25 percent smaller than at least one of the diameter, the ringwidth, and the ring height.
 16. Annular cornea implant for insertinginto a cornea pocket in the human eye via a narrow access to the pocketaccording to claim 1, wherein the adjustment force is in a range of0.001 N to 1 N.
 17. Annular cornea implant for inserting into a corneapocket in the human eye via a narrow access to the pocket according toclaim 1, wherein the ring body comprises a rigid material.
 18. Annularcornea implant for inserting into a cornea pocket in the human eye via anarrow access to the pocket according to claim 17, wherein the rigidmaterial is poly(methylmethacrylate).
 19. Annular cornea implant forinserting into a cornea pocket in the human eye via a narrow access tothe pocket according to claim 1, wherein the intermediate shape is asaddle-shape.